Tracking exploding lithium-ion batteries in real-time

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Tracking exploding lithium-ion batteries in real-time

http://www.sciencedaily.com/releases/2015/04/150428125253.htm

Date: April 28, 2015
Source: University College London

Summary: What happens when lithium-ion batteries overheat and explode has been tracked inside and out for the first time using sophisticated 3-D imaging. Understanding how Li-ion batteries fail and potentially cause a dangerous chain reaction of events is important for improving their design to make them safer to use and transport, say the scientists behind the study.

Exploding 18650.JPG

What happens when lithium-ion batteries overheat and explode has been tracked inside and out for the first time by a UCL-led team using sophisticated 3D imaging.

Understanding how Li-ion batteries fail and potentially cause a dangerous chain reaction of events is important for improving their design to make them safer to use and transport, say the scientists behind the study.

Hundreds of millions of these rechargeable batteries are manufactured and transported each year as they are integral to modern living, powering mobile phones, laptops, cars and planes. Although battery failure is rare, earlier this year, three airlines announced they will no longer carry bulk shipments of lithium-ion batteries in their cargo planes after the US Federal Aviation Administration tests found overheating batteries could cause major fires.

The study by UCL, ESRF The European Synchrotron, Imperial College London and the National Physical Laboratory, published in Nature Communications today, shows for the first time how internal structural damage to batteries evolves in real-time, and provides an indication of how this can spread to neighbouring batteries.

First author, UCL PhD student Donal Finegan (UCL Chemical Engineering), said: "We combined high energy synchrotron X-rays and thermal imaging to map changes to the internal structure and external temperature of two types of Li-ion batteries as we exposed them to extreme levels of heat. We needed exceptionally high speed imaging to capture 'thermal runaway' -- where the battery overheats and can ignite. This was achieved at the ESRF beamline ID15A where 3D images can be captured in fractions of a second thanks to the very high photon flux and high speed imaging detector."

Previously, X-ray computed tomography (CT) had only been used to analyse battery failure mechanisms post-mortem with static images and to monitor changes to batteries under normal operating conditions.

The team looked at the effects of gas pockets forming, venting and increasing temperatures on the layers inside two distinct commercial Li-ion batteries as they exposed the battery shells to temperatures in excess of 250 degrees C.

The battery with an internal support remained largely intact up until the initiation of thermal runaway, at which point the copper material inside the cell melted indicating temperatures up to ~1000 degrees C. This heat spread from the inside to the outside of the battery causing thermal runaway.

In contrast, the battery without an internal support exploded causing the entire cap of the battery to detach and its contents to eject. Prior to thermal runaway, the tightly packed core collapsed, increasing the risk of severe internal short circuits and damage to neighbouring objects.

Corresponding author, Dr Paul Shearing (UCL Chemical Engineering), said: "Although we only studied two commercial batteries, our results show how useful our method is in tracking battery damage in 3D and in real-time. The destruction we saw is very unlikely to happen under normal conditions as we pushed the batteries a long way to make them fail by exposing them to conditions well outside the recommended safe operating window. This was crucial for us to better understand how battery failure initiates and spreads. Hopefully from using our method, the design of safety features of batteries can be evaluated and improved."

The team now plan to study what happens with a larger sample size of batteries and in particular, they will investigate what changes at a microscopic level cause widespread battery failure.

Video: https://www.youtube.com/watch?v=uN8HcqAtDSY

Story Source:

The above story is based on materials provided by University College London. Note: Materials may be edited for content and length.
 
Those are really high temperatures that those cells wer exposed to. More like being in an external fire. I do wish they showed what happens when a cell is overcharged and how it will react internally.
otherDoc
 
docnjoj said:
Those are really high temperatures that those cells wer exposed to. More like being in an external fire. I do wish they showed what happens when a cell is overcharged and how it will react internally.
otherDoc
^^+1
Seems to me they are testing their equipment , more than the cells.
They are not going to learn much about 90% of cell failures, by cooking them in a furnace ! :roll:
They may as well analyse what happens to a can of gas if you sit it on a barbecue .
If cells are exposed to that temperature, you have a much bigger problem somewhere else !
 
Still valid to understand how the structure reacts when heated that much, but yeah, 1000 degrees is going to be tough on metals like copper or aluminum inside.

I still think the biggest problem is stuff like the hoverboards, the pack or the wiring after the pack not nearly able to handle the rough environment of real world shipping let alone actual use.

Cells themselves, provided the charger/bms works, are not too bad these days. But don't go shorting them.
 
Authentic name-brand "hoverboards" are bad enough, but...there was a recent story about how the customs department found and confiscated thousands of counterfeit hoverboards...I can only imagine how many make it through each month on aliexpress and ebay.

Crap cells with crap soldering and using a crap charger means for many people, their first hands-on experience with cheap lithium batteries will end with a smokey fire.
 
And then on top of that, as they learn to ride it, it goes flying across the room.

How long would you expect any battery to last, if you start out by throwing it at the wall?
 
Seems like it's just a matter of time before someone: gets launched off - knock themselves out - board bursts into flames - unconscious person burns to death - apartment burns down - others killed in apartment fire.
 
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